Abstract

The aim of the present study is to evaluate the severity of adhesions occurring after the use of different meshes for incisional hernia repair in rats. We assigned 37 female Wistar– Albino rats to four groups. A 2 × 2 cm abdominal wall defect was created in all rats. In Group 1 (Control), the peritoneum was closed with 4/0 polypropylene sutures. The abdominal wall defect was repaired with a condensed polytetrafluoroethylene mesh in Group 2, a polypropylene mesh coated with absorbable polydioxanone on the parietal side and oxidized regenerated cellulose on the visceral side in Group 3 and a PP mesh coated with carboxymethylcellulose and sodium hyaluronate on one side in Group 4. The abdominal wall with the adherent tissue was resected en bloc for macroscopic, histological and biochemical examinations. Fibrosis was significantly less severe in the control group than in the mesh groups, but did not significantly differ between the mesh groups. The average pressure required to break the resected mesh specimen was significantly lower in the control group than in the mesh groups, but did not significantly differ between the mesh groups. The mean hydroxyproline level was significantly lower in of Group 1 (Control) than in Groups 3 and 4 and in Group 2 than in Group 3. None of the meshes tested in this study was superior to the others in terms of severity of adhesions and incidence of complications. All three meshes, when placed in the peritoneum, resulted in more fibrosis than that in the control group.

Keywords

adhesion, hernia, incisional hernia, mesh

Introduction

In 1900, Witzel and Goepel first repaired hernias using a
material. In 1958, Usher used a polyamide mesh for hernia
repair, bringing in a new era in hernia surgery [1]. In recent
years, the incidence of incisional hernia has increased with
abdominal surgical interventions, and is 2–11% after median
incisions, 30–50% after primary repair and <15% after
repair with prosthetic materials [2]. The meshes are used at
the prepearing of the incisional hernias. All meshes have
both advantages and disadvantages, and no ideal mesh has
yet been found [3-6]. The most important disadvantage of
the meshes used in incisional hernia repair is the development
of massive adhesions between the mesh and the intraabdominal
organs, resulting in intestinal obstruction and
enterocutaneous fistula [5-7].

The characteristics of an ideal mesh have been identified
through experimental and clinical studies. Permeable prostheses are preferred to non-permeable prostheses, because
the former pose no risk of serum or lymphatic collection;
moreover, tissue growth into the mesh is easier, and
thus, prosthesis fixation is easy and does not require much
suturing. Monofilament materials are preferred owing to
their low infection risk. Contact of the prosthesis with internal
organs must be avoided. The prosthesis must cover
the hernia defect in such a way that it can be fixed to intact
tissue, so that the advantage of support of the normal abdominal
wall can be taken [8].

Various meshes have been developed as physical barriers
to prevent adhesions [10]. Polypropylene (PP) meshes are
made of non-absorbable, braided monofilaments. PP
meshes result in massive adhesions when placed directly
over the intra-abdominal organs, and may lead to severe
complications such as fistula [11,12]. Polytetrafluoroethylene
(PTFE) meshes are made of an expandable, nonbraided,
non-absorbable biocompatible material. Compared
to PP meshes, PTFE meshes rarely cause intraabdominal
adhesions, as their micropores help inhibit
tissue inflammatory response [4,5,13-15]. Therefore,
these meshes can even be used in the presence of an infection
[2]. Composite meshes consisting of a PP mesh
with hyaluronic acid–carboxymethylcellulose components
on one side of the mesh have been developed to prevent
the formation of adhesions. This composite mesh creates
a temporary barrier on the internal surface, while retaining
the strong penetration ability of PP meshes. Moreover,
this mesh is hydrophilic and soluble, and is resorbed
within a week [14,15]. A double-layer mesh consisting of
a PP mesh covered with absorbable polydioxanone (PDS)
on the parietal side and oxidized regenerated cellulose
(ORC) on the visceral side has also been developed [14].

Pharmacological agents that are used to prevent intraabdominal
adhesions either interfere in the steps of
wound healing, or prevent or treat the causes of adhesions
such as infection and exudate. Although these agents
prevent adhesion development to varying extents, the
success rate of all these approaches is limited [16,17].

In the current study, we study our purposes in a rat model
because of the similarty of rat's and human's anatomy.
And also, it is easier to grow and feed the rats than the
other animals for using in the experiments.

In the present study, intra-abdominal adhesions formed
after the use of different prosthetic materials for hernia
repair were investigated in a rat model of incisional hernia.
The severity of intra-abdominal adhesions and the
incidence of other complications were compared among
the different prosthetic materials via macroscopic, histopathological
and biochemical examinations.

Materials and Methods

This experimental study was conducted in 2009; the study
was approved by the ethics committee of our laboratory
and was in accordance with the standards of the European
Convention for the Protection of Vertebrate Animals used
for Experimental and Other Scientific Purposes (ETS 123).

Thirty-seven female Wistar–Albino rats were assigned to
four groups: three groups in which three different meshes
were used, with each group containing 10 rats, and a control
group of seven rats. The rats were subjected to intraperitoneal
anesthesia, and under sterile conditions, their abdominal skin was separated from the underlying muscle
and fascia through a median incision to create a 2 × 2 cm
defect.

In the control group (Group 1), only an inlay suture was put
on the four edges of the peritoneum using 4/0 polypropylene
(Prolene®, Ethicon Inc., Somerville, New Jersey). The
skin was closed by continuous sutures with 3/0 polypropylene.
In the mesh groups, the abdominal wall defects were
repaired using 2 × 2 cm, pre-prepared meshes as follows:
Group 2, condensed PTFE (MotifMesh™, Proxy, Biomedical
Limited, Galway, Ireland; Figure 1); Group 3,
double-layer PP mesh covered with absorbable PDS on the
parietal side and ORC on the visceral side (Proceed®, Ethicon)
and Group 4, PP mesh with hyaluronic acid and carboxymethylcellulose
components on one side (Sepramesh
®, Genzyme Surgical Prd., Cambridge, MA). The
abdominal skin was closed using continuous sutures with
3/0 polypropylene after the meshes were placed into the
peritoneum (inlay) in a primary fashion and fixed with 4/0
polypropylene sutures.

Figure 1: After repair in Group 2.

The rats were monitored for 28 days to check for weight
loss, decreased food and/or water intake and infection.
They were sacrificed on postoperative day 28. The abdominal
skin over the fascia was decollated in order to not
damage the surgical line. The anterior abdominal wall was
opened via a wide, concave, full-thickness incision such
that the fascial defect and the mesh could be explored from
2 cm below.

The incision and any adhesions between the mesh and
intra-abdominal organs were evaluated using the macroscopic
intra-abdominal adhesion scoring system proposed
by Mazuji et al. [18]. The macroscopic adhesions were
classified with the system identified by Majuzi [18]. Classification
system is like that: a) No adhesion; score 0. b) Thin
or narrow, easily separable adhesions; score 1. c) Adhesions
limited to a small area; score 2. d) Thick adhesions
dispersed over a large area; score 3. e) Thick and wide
adhesions, adhesions of the organs to the anterior and/or
posterior abdominal wall; score 4. Migration of the prosthetic
material and presence of enterocutaneous fistula
were also evaluated.

The remaining 2 × 1 cm of the mesh along with the adherent
tissue was harvested, and the pressure required to break
the specimen was recorded in kilograms using a tensiometer. Thereafter, the specimens were placed in normal saline
and sent to a biochemistry laboratory for hydroxyproline
assessment. Tissue hydroxyproline levels in the materials
sent were measured using high-performance liquid chromatography
in milligrams per liter per gram tissue.

Statistical analyses were performed using the NCSS 2007
package program. Data were evaluated with the Kruskal–
Wallis test (KW) for intergroup comparisons and with
Dunn’s multiple comparison test for subgroup comparisons.
Quantitative data were compared using the chisquare
test. Statistical significance was set at p < 0.05.

Results

No deaths, surgical wound infections or weight loss occurred
in the subjects during the study. The results of
macroscopic evaluation of the adhesions are summarized
in Table 1 (Figure 2). Statistical comparison of the
macroscopic adhesion score among the study groups revealed
a χ2; value of 14.4 and a p value of 0.275. No statistical
differences were observed between the four groups in terms of distribution of macroscopic intra-abdominal
adhesion scores (p = 0.275).

Using light microscopy, we assessed the tissue samples
using the fibrosis (Table 2) and inflammation scoring
systems (Table 3) used by Hooker et al. [10]. Statistical
comparison of the groups and p values in terms of fibroblast
density were as follows: Group 1 (Control) vs.
Group 2, 0.009; Group 1 (Control) vs. Group 3, 0.007;
Group 1 (Control) vs. Group 4, 0.012; Group 2 vs. Group
3, 0.653; Group 2 vs. Group 4, 0.653; and Group 3 vs.
Group 4, 0.371. Significant differences were found
among the fibrosis scores of Groups 1–4 (p = 0.0001). A
score of 0 was significantly more common in Group 1
(Control) than in Groups 2–4 (p = 0.009, p = 0.007 and p
= 0.012, respectively). No differences in fibrosis scores
were found between the other groups (p > 0.05). Statistical
comparison of the inflammation scores in the various
study groups revealed a χ2; value of 5.55 and a p value of
0.475. No significant difference was observed in the distribution
of inflammation scores among Groups 1–4 (p =
0.275).

Table 2: Distribution of fibrosis scores among the study groups.

Table 3: Distribution of inflammation scores among the study groups.

The statistical comparison of the breaking pressures, as
assessed using a tensiometer, in the various groups is
presented in Table 4. Significant differences in mean
breaking pressure were observed among Groups 1–4 (p = 0.007). The mean breaking pressure was significantly
lower in Group 1 (Control) than in Groups 2–4 (p =
0.001). No statistical differences in mean breaking pressure
were found among the other groups (p > 0.05).

Table 4: Statistical comparison of breaking pressures.

The statistical comparison of hydroxyproline levels among
the groups is presented in Table 5. Significant differences
in mean hydroxyproline levels were observed among
Groups 1–4 (p = 0.0001). The mean hydroxyproline level
was significantly lower in Group 1 than in Groups 3 and 4
(p = 0.001 and p = 0.01, respectively) and in Group 2 than
in Group 3 (p = 0.015). No other statistical differences
were observed among the groups (p > 0.05).

Table 5: Statistical comparison of hydroxyproline levels between the groups.

Mesh migration, which was one of the complications
assessed macroscopically, was not observed in Groups 1
(Control) and 2, but was present in four subjects in Group
3 and three subjects in Group 4. No significant difference
was found between the groups in terms of presence of
migration (p = 0.055). Similarly, there were no statistical
differences among the four groups in terms of presence of
fistula (χ2: 2.77; p = 0.427). Fistula was detected in only a
single subject in Group 3.

Discussion

Incisional hernias are encountered as a complication of
abdominal surgical interventions and are a type of iatrogenic
hernia. Prosthetic materials (meshes) that are used
for the repair of incisional hernia frequently lead to intraabdominal
adhesions due to the intense inflammatory
response that these materials elicit. The resulting adhesions
cause intestinal obstruction, chronic abdominal pain
and enterocutaneous fistula, as well as difficult resurgeries
and infertility in women [19].

Peritoneal trauma such as surgery is the main cause of
intra-abdominal adhesion. Ischemia and the presence of a
foreign body enhance the development of adhesions
[20,21]. Minimally invasive surgical techniques, including
laparoscopic techniques, are being developed to reduce
the likelihood of intra-abdominal adhesions after
incisional hernia repair. In addition, prostheses made of
different materials in different designs are also being
investigated for use in modern hernia surgery. In order to
reduce adhesions via current approaches, peritoneal trauma
should be reduced, inflammatory response and coagulation
should be inhibited and surfaces that are likely to
form adhesions should be cleaned to inhibit fibrosis [9].

Currently, a double-layer PP mesh covered with absorbable
PDS on the parietal side and ORC on the visceral
side (Proceed®), a PP mesh that includes hyaluronic acid
and carboxymethylcellulose components on one side
(Sepramesh®) and a condensed PTFE mesh (Motif-Mesh™) are frequently used in incisional hernia repair
when primary closure of the peritoneum and fascia is not
feasible. The present study macroscopically, histopathologically
and biochemically compared these three
frequently used meshes in terms of their capacity to elicit
intra-abdominal adhesions.

The three mesh groups (Groups 2–4) were compared with
a control group and with each other in terms of macroscopic
adhesions, and macroscopic intra-abdominal adhesions
of varying severity were detected in 79.3% of the
cases. However, none of the groups was statistically superior
to the others. Voskerician et al. compared condensed
PTFE with the double-layer PP mesh used in this study, in
terms of adhesions and found the former to be superior
[22]. Burger et al. found that a PP mesh with hyaluronic
acid and carboxymethylcellulose components on one side
was superior to the double-layer PP mesh [23].

In our study, histopathological examination revealed that
a fibrosis score of 0 was significantly more common in
Group 1 (Control) than in the mesh groups, and that the
incidence of this score was similar among the mesh
groups, indicating that fibrosis during wound healing was
enhanced in the presence of a foreign body in contact
with the peritoneum. Inflammation was found in all the
study groups, with an inflammation score of 1 in 56.8%
of cases. However, none of the groups was found to be
superior to the other in terms of inflammation.

In our study, mean hydroxyproline levels significantly
differed between the four groups (p = 0.0001). This level
was significantly lower in Group 1 (Control) than in
Groups 3 and 4 (p = 0.001 and p = 0.01, respectively) and
in Group 2 than in Group 3 (p = 0.015). No other significant
differences were observed between the groups (p >
0.05).

Mesh migration occurred in Groups 3 and 4, and its incidence
in these two groups was statistically similar. Fistula
occurred in only a single subject in Group 3, with no
significant differences between the groups. Numerous
complications have been reported with the use of mesh
materials and include infection, chronic sinuses, intraabdominal
adhesions, enterocutaneous fistula, intestinal
obstruction, malnutrition and hernia recurrence [24].

Conclusion

We compared a double-layer PP mesh covered with absorbable
PDS on the parietal side and with ORC on the
visceral side (Proceed®), a PP mesh with hyaluronic acid
and carboxymethylcellulose components on one side
(Sepramesh®) and a condensed PTFE mesh (Motif-
Mesh™) in terms of the severity of adhesions and other
complications, by using macroscopic, biochemical and histopathological examinations. None of the meshes was
superior to the others. On biochemical examination, intraabdominal
adhesions were less severe with the condensed
PTFE mesh than with the double-layer PP mesh. However,
all three meshes, when placed in the peritoneum,
resulted in more severe fibrosis than that in the control
group. Further clinical and experimental studies are required
to develop an ideal mesh that would minimize
intra-abdominal adhesions.